1. Field of the Invention
The present invention relates to an electric circuit arrangement and method for checking the intactness of a photodiode array and the intactness of an electrical connection between the array and a microprocessor. Such microprocessor being spatially separated from the array and being provided to evaluate an output signal of the array. Such output of the array having a high resistance or high impedance in the inactive, intact state and, in case of an error, being connected via in each case a defined internal resistance to a ground or a supply voltage potential.
2. Background Art
Photodiode arrays of the relevant type include a linear or planar arrangement of a multiplicity of photosensitive elements or sensors, generally designated as pixels, on a semiconductor chip or the like. Each of these pixels generates and provides an analog output signal representing the quantity of light incident on the pixel. Photodiode arrays are used in a number of optical sensor applications in which brightness information is required with spatial resolution. The analog output signals of the individual pixels are generally read out in sequence from the chip based on clock pulses and are then fed to an analog/digital converter (ADC) input of a microprocessor. The microprocessor converts the analog output signals of the individual pixels into digital signals or digital brightness values. An evaluation algorithm suitable for the particular application then processes the digital brightness signals further.
A possible application in particular of a row-based photodiode array is, e.g., an optoelectronic angle of rotation sensor, as is used, for instance, as a steering angle sensor in motor vehicles.
A sensor of this type is known from DE 40 22 837 A1. The steering angle sensor described in this document includes an electronic control unit and a sensor unit. The sensor unit includes two parallel elements arranged at a distance from one another—a light source and a row sensor—. The sensor unit further includes an encoder disk arranged between the light source and the row sensor. The encoder disk is locked to the steering column. The row sensor for the row-based photodiode array is a CCD sensor row.
In the encoder disk, an Archimedean spiral extending over 360° and formed as an optical slot is provided for encoding purposes. Based on the exposure of corresponding converter elements in the row sensor at a specific steering angle, the actual steering position can be determined. The Archimedean spiral used for encoding purposes is formed to extend continuously so that it can be addressed as an analog encoding. With the same arrangement, however, a digital encoding can also be read out equally well on the encoder disk, which can be implemented, for example, in the form of a gray code.
Due to space restrictions, it is often necessary in such applications to arrange the actual sensor unit, i.e., the row sensor and the light source, spatially separate from the associated electronic control and evaluation unit. This requires a more or less long electrical connection line between the units. The electrical connection line can be implemented in the form of plug contacts, foil conductors, etc. However, this connection always represents a potential source of additional errors which can manifest themselves, for example, in the form of contact problems or line cracks.
Conventional photodiode arrays do make it possible to directly assess the component itself based on the status of the output signal, but an undefined state will be present at a remotely arranged evaluation unit in case of an interruption to the electrical connection line.